1. Field of the Invention
The present invention relates to a transmitting method and system suitable for a data transmission between devices connected through a bus line having an IEEE 1394 method, for example, and a transmission control device applying the transmitting method.
2. Description of the Related Art
There has been developed an AV device capable of mutually transmitting information through a network using a serial data bus having the IEEE 1394 method. When a data transmission is to be carried out through the bus, an isochronous transportation mode to be used for real-time transmitting dynamic image data, audio data and the like which have comparatively large capacities and an asynchronous transportation mode to be used for surely transmitting a static image, text data, a control command and the like are prepared and a special band for each mode is used for the transmission, and the transmission in both modes can be mixed on one bus.
When the data transmission is to be carried out in the asynchronous transportation mode, a connection establishment processing for ensuring a transmission path between a data transmitting device and a data receiving device on the bus is executed under the control of a device referred to as a controller which is connected to the bus and the data transmission is performed between both devices through the ensured transmission path. In the following description, the data transmitting device connected to the bus will be referred to as a producer and the data receiving device connected to the bus will be referred to as a consumer.
A connection establishment processing between the producer and the consumer is executed by the controller based on a predetermined protocol. For example, the producer and the consumer are connected with point to point (P to P) through the transmission of a command defined by an AV/C command. After the connection is completed, data having a segment structure are successively transmitted from the producer to the consumer at the request of the consumer. When all the data are completely transmitted, the P to P connection is cut out through the transmission of a command under the control of the controller.
Thus, various data can be transmitted between optional devices connected through the serial data bus having the IEEE 1394 method. An AV/C command set is standardized with 1394 TA (Trade Association) and the details of the AV/C command are opened to the public through http://www.1394.org.
When the controller is to control the data transmission in the asynchronous transportation mode or the like between the devices connected through the serial data bus having the IEEE 1394 method, a device to function as the controller should mount a function corresponding to the data transmission to be carried out at that time. More specifically, any device connected to the bus does not function as the controller and only a device mounting a function corresponding to the setting method of the transmission path at that time can carry out a processing as a controller for performing the corresponding control.
If all the devices in a network connected through the bus mount the function of the controller, any device in the network can freely set the transmission path so that the degree of freedom of the data transmission in the network can be enhanced. However, when the function of the controller is mounted on all the devices in the network, the mounting function of each device is increased correspondingly. Consequently, there is a problem in that a cost for each device and the whole network is increased.